Question

preciso de ajuda.

a) x+y=20
x-y=8

b) 3x-y=18
x+y=10

c) x+y=32
x-y=18

d) 6x-y=20
4x+3y=40

e) 7x+6y=23
5x+6y=21

f) 8x+5y=11
4x+5y=3

Answer 1

a)

x+y=20

x-y=8 (+)

------------

2x = 28

x = 28/2

x = 14

x + y = 20

14 + y = 20

y = 20 - 14

y = 6

b)

3x-y=18

x+y=10 (+)

-----------------

4x = 28

x = 28/4

x = 7

x + y = 10

7 + y = 10

y = 10 - 7

y = 3

c)

x+y=32

x-y=18 (+)

-----------------

2x = 50

x = 50/2

x = 25

x+y = 32

25+y = 32

y = 32 - 25

y = 7

d)

6x-y=20 . (3)

4x+3y=40

18x - 3y = 60

4x + 3y = 40 (+)

---------------------------

22x = 100 (:2)

11x = 50

x = 50/11

4x + 3y = 40

4.50/11 + 3y = 40

200/11 +3y = 40

(200 + 11.3y)/11 = 11.40/11

200 + 33y = 440

33y = 440 - 200

33y = 240

y = 240/33

e)

7x+6y=23

5x+6y=21 (-1)

7x + 6y = 23

-5x - 6y = - 21 (+)

-------------------------

2x = 2

x = 2/2

x = 1

7x + 6y = 23

7.1 + 6y = 23

7 + 6y = 23

6y = 23 - 7

6y = 16 (:2)

3y = 8

y = 8/3

f)

8x+5y=11

4x+5y=3 (-1)

8x + 5y = 11

-4x - 5y = - 3 (+)

-------------------------

4x = 8

x = 8/4

x = 2

8x + 5y = 11

8.2 + 5y = 11

16 + 5y = 11

5y = 11 - 16

5y = - 5

y = -5/5

y = - 1